blast: Fix the error in `stat' Errno::ENOENT

mv gives the error message:
fileutils.rb:1552:in `stat'
Errno::ENOENT: No such file or directory -
$HOMEBREW_PREFIX/Cellar/blast/2.2.28/lib/libaccess-static.a
Does not work: mv Dir[lib / 'lib*.a'], libexec
Works: system "mv #{lib}/lib*.a #{libexec}/"
blast: Add the option --disable-tests